THIS INVENTION relates to a method of and apparatus for manufacturing non-woven fabrics and, in particular, geotextiles.
Non-woven geotextiles are sheet materials which are constructed from synthetic fibres, made of polypropylene and/or other synthetic materials, and are employed in civil engineering applications, such as land drainage, filtration and reinforcement.
In a known production line for manufacturing non-woven geotextiles, quantities of different input fibres to be incorporated in the non-woven product in predetermined proportions are first weighed out by an electronically controlled weighing machine. The constituent input fibres are then subjected to an initial opening and mixing operation in a main opening machine, the opened and mixed fibres then being passed into a mixing and blending bin in which the fibre-to-fibre mixing is improved to optimise the uniformity of the mixture of input fibres. The output of the mixing and blending bin next enters a fine opening machine which ensures that the input fibres are fully opened and blended into a homogeneous mixture to ensure that the finished product has a consistent density. The input fibre mixture emerging from the fine opening machine is transferred to a hopper which includes a vibrating system accurately controlled by photosensitive detectors to deliver a continuous flow of the fibre mixture at a constant flow rate into a carding machine which serves to comb and straighten the mixture of input fibres to form a carded web of desired thickness. The carded web delivered by the carding machine is then deposited as overlapping layers onto a conveyor travelling transversely of the length direction of the carded web by a cross-lapping machine to form a layered web. The conveyor transports the layered web to a series of needle-punching machines which securely interlock and entangle the fibres of the overlapping layers to form a non-woven geotextile strip which is wound into a roll of the required size by a winding machine after leaving the last needle-punching machine.
In the described process, the production line up to the cross-lapping machine is orientated in the length direction of the product. Consequently, the carded web leaving the carding machine inevitably has weaker strength properties in the length direction than in the width direction. Since the length direction then becomes the width direction in the layered web as a result of the action of the cross-lapping machine, the result is that the strength of the finished geotextile product is impaired to some degree in the width direction. Whilst the known process is capable of producing geotextile products having a strength in the width direction which is adequate for many purposes, there are also many circumstances in which a geotextile product having greater strength in the width direction would be desirable.
It is accordingly an object of the present invention to provide a method of and apparatus for manufacturing a length of non-woven fabric which provide the fabric with enhanced the strength in the width direction.
Accordingly, in one aspect, the present invention provides a method of manufacturing a non-woven fabric, comprising: opening and mixing different input fibres to form a uniform fibre mixture having predetermined proportions of the different input fibres; carding the fibre mixture to form a uniform web of predetermined thickness travelling in a first direction; depositing fixed lengths of the web in alternating fashion on a conveyor travelling in a second direction transverse to the first direction to form on the conveyor a mat consisting of overlapping lengths of the web; and needle-punching the mat to form the non-woven fabric; which method is characterised by laying high tenacity yarns onto the web prior to depositing the lengths of the web on the conveyor to form the mat, the yarns extending in the first direction and being spaced apart transversely of the first direction.
Conveniently, the high tenacity yarns are dropped onto the web as the web leaves the carding machine.
In one method embodying the invention, which strengthens the non-woven fabric both in the second direction and transversely of the second direction, each high tenacity yarn is laid on the web so that the yarn both extends along the first direction and undulates transversely of the first direction.
In carrying out a method embodying the invention, the spacing of the yarns transversely of the first direction may be selected to achieve a desired increase in the strength of the non-woven fabric transversely of the second direction.
Preferably, the high tenacity yarns comprise yarns made from one or more materials selected from the group consisting of polyester, aramide and glass fibre.
In another aspect the invention provides apparatus for manufacturing a non-woven fabric, comprising: an opening and mixing arrangement for opening and mixing input fibres to form a uniform fibre mixture having predetermined proportions of different input fibres; a carding machine for carding the fibre mixture to form a uniform web of predetermined thickness travelling in a first direction; a cross-lapping machine for depositing lengths of the web in alternating fashion onto a conveyor travelling in a second direction transverse to the first direction to form on the conveyor a mat consisting of overlapping lengths of the web; and needle-punching the mat to form the non-woven fabric; which apparatus is characterised by yarn applying means for laying high tenacity yarns onto the initial web prior to depositing the lengths of the web onto the conveyor, the yarns extending in the first direction and being spaced apart transversely of the first direction.
Conveniently, the yam applying means drops the high tenacity yarns onto the web as it leaves the carding machine.
In one apparatus embodying the invention, the yam applying means lays each high tenacity yam on the web so that the yam both extends along the first direction and undulates transversely of the first direction, thereby strengthening the non-woven fabric both in the second direction and in transversely of the second direction.
Advantageously, the yarn applying means is adjustable to vary the spacing of the high tenacity yarns and thereby vary the strength of the resulting non-woven fabric.
Preferably, the high tenacity yarns are made from one or more materials selected from the group consisting of polyester, aramide and glass fibre.
In a further aspect, the invention provides a non-woven fabric made by the method of the present invention.